1. Field of the Invention
The present invention relates to a method of making a white LED package structure having a silicon substrate, and more particularly, to a method of making a white LED package structure having a silicon substrate with good thermal conductivity and good light condensation to raise the color rendering and the colorfulness of tone.
2. Description of the Prior Art
In recent years, a white LED is a new product that is most expected and focused on worldwide. The white LED has advantages of small volume, no radiation, low power consumption, long lifetime, fast response rate and functions of environment protection etc., and also can solve many past problems that incandescent lamps could not overcome. Therefore, scientists in Europe and America have served the white LED as a light source in 21 century.
Please refer to FIG. 1. FIG. 1 is a cross-sectional schematic diagram of a white LED package structure according to the prior art. The white LED package structure 10 comprises a blue LED 11, a substrate 12, two electrodes 13, 14, a conductive layer 15 and a phosphor structure 16. The blue LED 11 is a main light-emitting element of the white LED package structure 10. The conductive layer 15 can be disposed on the substrate 12 by the process of metal deposition, exposure and lithography etc., and the blue LED 11 can be electrically connected to the electrodes 13, 14 through the conductive layer 15. The phosphor structure 16 is used for preventing the blue LED 11 from being directly exposed to the exterior, and the phosphor powders doped in the phosphor structure 16 including epoxy resin has a function of absorbing the blue light and converting blue light to yellow light. Therefore, a portion of blue light emitting from the blue LED 11 will be absorbed and converted to yellow light by the phosphor structure 16, and the yellow light will be mixed with the other portion of the blue light so that white light is produced.
The defect in current technology is that only one blue LED is disposed in the white LED package structure 10. If a brighter illumination or a larger size of light source is required, to combine several white LED package structures 10 is necessary. However, one white LED package structure 10 has a specific size, so the size of the light source is much larger. In addition, the full width at half maximum (FWHM) of the wavelength of one blue LED is about 25 nm. In manufacturing process, a great deal of the blue LEDs cannot be made to all have the same wavelength. Therefore, the produced blue LEDs currently can be divided into three specifications by the wavelengths of the blue LEDs, and the specifications are 450±5 μm, 460±5 μm and 470±5 μm. In accordance with the three specifications, the three corresponding phosphor powders are respectively created to produce the white LED. However, because the condition of manufacturing the blue LEDs is not easy to control, the wavelength of the blue LED will easily have a deviation effect. Even using the blue LED with the same specification, the produced white LEDs still will have various tones of the white light. The color rendering of the white LED is lower than that of fluorescent lamps and incandescent lamps, and the colorfulness of tone of the white LED is, too. Therefore, to produce a white LED having high color rendering and colorful tone to match the natural light is an object that needs the industry to improve.